I feel like swarms of ants are crawling all over my leg when I try to sleep. What’s happening to me? DR MARTIN SCURR has the troubling answer

When I try to sleep my lower left leg feels as though swarms of ants are crawling all over it, then my toes seem to go solid! My right leg is perfectly normal. A friend suggested it was restless legs syndrome, but I don’t feel the need to move my leg. Despite three visits to doctors, they can offer no solution. At 90 this sleeplessness is a problem.

Audrey Brookes, Nottingham.

The technical term for your symptoms – the sensation of insects crawling on the skin – is formication. It’s caused by an underlying nerve problem, in this case involving the nerve supply to your left leg.

My first suggestion is that it might be a form of sciatica – irritation or partial entrapment of the sciatic nerve, possibly relating to a problem in the lumbar (or lower) spine, such as arthritis or a damaged disc (but that makes itself known when you lie down).

Sometimes arthritis of the hip can also affect the sciatic nerve, as it runs close to the joint. However, I’d suggest in your case this is unlikely as you’d know if you had an arthritic hip, as it causes stiffness and alters your gait and posture.

I agree the symptoms don’t sound like the usual manifestations of restless legs syndrome: as you correctly point out, this is characterised by an irresistible urge to move your legs.

Another possibility is peripheral neuropathy (damage to nerve function), usually in the legs. This can be a complication of diabetes, vitamin B12 deficiency, and some medical conditions such as an underactive thyroid – although it would be very uncommon to have this symptom on just one side for any length of time.

Nerve damage can also be a side-effect of some antidepressants and antipsychotics (and stimulants such as cocaine) but, again, this would be unlikely to affect only one side.

I suggest asking your GP about your spine and hip joint – at the very least a simple X-ray of your lumbar spine might help in assessing whether you’re in fact suffering from a form of sciatica that doesn’t cause pain.

Should this be the diagnosis, treatment might include medication, or possibly surgery.

Last year, my husband, 85, was diagnosed with an inoperable tumour on his pancreas, after undergoing investigations for a blocked bile duct. But he has developed a persistent cough which I fear may be due to Creon, a drug he has been prescribed to help him digest food. Is there an alternative medication he could try?

S. Morgan, Caerphilly.

I admire your resilience and the strength involved in caring for your husband through this very worrying time.

Your letter implies that the tumour was found at the head (the rounded end) of the pancreas, which would disrupt the normal flow of bile through the bile duct. It is also very likely that the flow of digestive enzymes secreted by the pancreas was greatly reduced, if not completely disrupted.

These enzymes – along with bile salts – help with digesting food, in particular fats, which is why your husband was prescribed Creon, a capsule containing digestive enzymes taken with meals. Though it can lead to abdominal pain, bloating, nausea and bowel upset, I can find no evidence that Creon causes a cough.

In your longer letter, you mention this settled when your husband stopped taking Creon, partly because of the side effects but also because it’s difficult to get hold of at the moment. (He also started taking a supplement, L-glutamine – however, this is a red herring as L-glutamine has no influence on digestion or absorption of food.)

Your husband needs to get as much nutrition as possible from his food. I would encourage you to get him back on a pancreatic supplement.

There are alternatives to Creon, such as Nutrizym and Pancrex. As your husband has been weak – no doubt due to the development of the pancreatic mass – I hope his strength and vitality is restored soon.